Title: Combined Effects Chamber – Multivariate Agile Test Methodologies to Produce Real-World Results
Author: C.Y. Ingham
Aircraft are routinely exposed to an extreme array of environmental conditions including changes in relative humidity, exposure to ultraviolet (UV) light, temperature fluctuations, corrosive environments, and reactive gases prevalent at altitude (e.g., ozone) over the course of their service lifetime. Coatings, sealants, composites, and other high performance materials utilized in aircraft manufacture must be designed to withstand repeated exposures to these conditions in order to mitigate part degradation or failure, and minimize associated repair work. Material manufacturers design and develop each element of a coating system to pass Standard Salt Spray Fog Tests (ASTM B117) and Department of Defense Environmental Lab Tests (MIL-STD-810 509.5). Aircraft manufacturers then select these materials based on ASTM and MIL specifications, where the best performing products are recommended. These standard salt-fog tests typically test to failure, rather than actual material performance, and correlate the laboratory results to outdoor exposure in extreme environments, with very poor correlation in coating performance (less than 0.9 chi-squared test value). While rigorous and capable of exposing premature failure, these methods of material testing are fundamentally lacking in terms of applicability, as the qualification process does not expose test articles to combinations of environmental factors that are experienced in flight that can and will lead to accelerated coating degradation once put into actual service. A better assessment tool to qualify aircraft materials and understand corrosion-initiating mechanisms is necessary.
Outline of the key points to be made :
- B117 background
- Correlation of current test methods to outdoor and real-world
- Importance of chrome-free systems and distinction between chromate primers and the new class of chrome-free primers
- Correlation strategy including environmental characterization and monitoring, cumulative corrosion damage modeling, outdoor exposure and teardown, and in-situ monitoring.
- Future test method development expanding and accelerating capabilities of pass-fail coating stackup testing
Conclusions or recommendations: Systems & Materials Research Corporation (SMRC) is developing their Programmable Accelerated Environmental Test System to give coating developers, coating system specifiers, airframe accelerated testing providers, and airframe manufacturers a platform to design new materials to in order to better predict their service performance. Working under a Phase I Small Business Innovation Research (SBIR) contract, SMRC developed a prototype chamber with the ability to subject test specimens to corrosive conditions; 95% NaCl spray, NO2, CO2, UV light, ozone, and temperature cycling. SMRC is currently developing a Phase II chamber to further progress this technology with the goal of fabricating a fully functional product by project end. The envisioned system will have the capability to subject test specimens to a complex mixture of environmental elements simultaneously to simulate real-world conditions, with feedback monitoring, control, and logging, to reach a Manufacturing Readiness Level (MRL) of 6. SMRC’s advanced test chamber will require materials able to withstand extreme temperatures and ozone levels as well as potential chemical interactions caused by multiple gaseous species within the chamber environment. Furthermore, requirements to produce 3× solar irradiation within the chamber necessitates extensive development of UV light configurations in addition to providing corrosion evaluation capabilities and a stress/strain test fixture for corrosion samples.